Pneumatic tire with specified bead toe

ABSTRACT

A pneumatic tire is disclosed, which comprises: (1) a reinforcing rubber layer made of short fiber reinforced rubber, alternatively (2) a reinforcing rubber layer having hardness set in a range of 90° to 99° of JIS-A hardness, which is arranged in an area of a bead section from a bead toe section along a tire inner wall surface, and wherein a chafer composed of an organic fiber cord having a high strength and a high elastic modulus is provided to cover an outer side of the reinforcing rubber layer from the tire inner wall surface to the bead toe area.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a pneumatic tire having improvedturnability during high speed running. More specifically, the inventionrelates to a pneumatic tire which is suitably used for racing.

[0002] With heightened vehicular performance in recent years, furtherimprovement has been demanded for tire turnability during high speedrunning. Specifically, an excessive lateral force is applied to an outerside of a turning tire when a vehicle is turned during high speedrunning, and a side section and a bead section outside the vehicle fallto the inner side of the tire. Consequently, limitation is put onturnability.

[0003] Conventionally, efforts have been made to improve turnabilityduring high speed running by preventing falling of the bead sectionduring turning. For example, a bead section structure was presented(Japanese Unexamined Patent Laid-Open No. 6 (1994)-227216), which uses abead core made of single strand steel, and includes a rubber stockhaving hardness set in a range of 80° to 98° of JIS-A hardness andarranged in a bead toe section, and a chafer composed of an organicfiber cord and arranged on an outer surface of the rubber stock.

[0004] However, the foregoing bead section structure has been unable tosatisfy a recent demand for further speeding-up. For example, it isimpossible to secure driving stability when a vehicle is run on a cornerof a 100 m radius at a high speed of 200 km/h.

SUMMARY OF THE INVENTION

[0005] An object of the present invention is to provide a pneumatic tirecapable of securing high speed turnability, for example, when a vehicleis run on a corner of a 100 m radius at a high speed of 200 km/h orhigher.

[0006] In order to achieve the foregoing object, the present inventionprovides a pneumatic tire which comprises carcass layers providedbetween a pair of bead cores buried one in a left bead section and theother in a right bead section and a belt layer arranged outside thecarcass layers and around a tire in a tread section and wherein areinforcing rubber layer made of short fiber reinforced rubber isarranged in an area of the bead section from a bead toe section along atire inner wall surface.

[0007] Also, in order to achieve the object, the present inventionprovides a pneumatic tire comprising carcass layers provided between apair of bead cores buried one in a left bead section and the other in aright bead section and a belt layer arranged outside the carcass layersand around a tire in a tread section, and wherein a reinforcing rubberlayer having hardness set in a range of 90° to 99° of JIS-A hardness isarranged in an area of the bead section from a bead toe section along atire inner wall surface and a chafer composed of an organic fiber cordis provided to cover an outer side of the reinforcing rubber layer fromthe tire inner wall surface to a bead seat, the organic fiber cordhaving a strength of 0.25 KN/cord or higher and an elastic modulus of 20KN/mm² or higher.

[0008] In the pneumatic tire of the present invention, an area of thebead section from the bead toe section to the tire inner wall surfaceincludes (1) a reinforcing rubber layer made of short fiber reinforcedrubber, alternatively (2) a reinforcing rubber layer having hardness setin the range of 90° to 99° of JIS-A hardness, and an outer side of thereinforcing rubber layer is covered with a chafer composed of an organicfiber cord from the tire inner wall surface to the bead seat area, theorganic fiber cord having strength of 0.25 KN/cord or higher and anelastic modulus of 20 KN/mm² or higher. Accordingly, even when a vehicleis turned on a corner of a 100 m radius at a high speed of 200 km/h orhigher, since the reinforcing rubber layer of the bead toe sectionexhibits a high compressive strength to suppress large deformation ofthe tire side section, turnability can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a sectional view of a tire meridian direction showing anexample of a bead section of a pneumatic tire of the present invention;

[0010]FIG. 2 is a view showing a relationship between a width L₂/L₁ andturnability during high speed running;

[0011]FIG. 3 is a view showing a relationship between an angle θ andturnability during high speed running;

[0012]FIG. 4 is a view showing a relationship between a height H/a widthL₁ and turnability during high speed running;

[0013]FIG. 5 is a sectional view of a tire meridian direction, showinganother example of a bead section of a pneumatic tire of the presentinvention;

[0014]FIG. 6 is a view showing another relationship between a widthL₂/L₁ and turnability during high speed running;

[0015]FIG. 7 is a view showing another relationship between an angle θand turnability during high speed running; and

[0016]FIG. 8 is a view showing another relationship between a height H/awidth L₁ and turnability during high speed running.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] (1) FIG. 1 is a sectional view of a tire meridian direction,showing one side of a bead section which constitutes a pneumatic tire ofthe present invention used as a racing tire. Regarding a bead sectionlike that shown in FIG. 1, a pair of such bead sections 1 are providedin both left and right sides. Two carcass layers 3 ₁ and 3 ₂ are putaround a bead core 2 which is buried in the beat section 1. An end ofthe innermost carcass layer 3 ₁ is folded around the bead core 2 from atire inner side to an outer side and wound up. The end part of thecarcass layer 3 ₁ is then positioned in the middle part of a bead filler8. On the other hand, the outermost carcass layer 3 ₂ is arranged alongand outside the wound-up part of the carcass layer 3 ₁ to reach a tip ofa bead toe section 4. In a tread section, a plurality of belt layers(not shown) are arranged outside the carcass layers 3 ₁ and 3 ₂ andaround a tire. Reference numerals 7 ₁ and 7 ₂ denote reinforcing layersmade of organic fiber cords.

[0018] The bead toe section 4 includes a reinforcing rubber layer 6,which is extended from a tire axial direction inner side area of thebear core 2 along the bead filler 8 to a position near the tip thereof.The reinforcing rubber layer 6 is made of rubber (short fiber reinforcedrubber), which is reinforced by short fibers 5.

[0019] No particular limitation is put on a kind of a short fiber 5, andany can be used as long as it has reinforcing capability. For example,one selected from a polyester fiber, a nylon fiber, a vinylon fiber, acarbon fiber, a glass fiber, an aromatic polyamide fiber, and so on, canbe used. A length of this short fiber should not be too short or toolong. Preferably, the length should be set in a range of 0.2 mm to 6.0mm. An average diameter of the short fiber 5 should preferably be setequal to 15μ or lower.

[0020] No particular limitation is placed on a ratio of blending shortfibers and rubber for the reinforcing rubber layer 6. Preferably,however, 5 to 30 parts weight of short fibers should be blended withrespect to 100 parts weight of rubber. When necessary, compoundingagents such as carbon black or the like may be blended. Further, in thereinforcing rubber layer 6, the short fibers should preferably beoriented mainly in a tire radial direction. This orientation canincrease a compressive strength of the reinforcing rubber layer 6 moreand flexural rigidity thereof. Accordingly, turnability can be improved.Preferably, hardness of the reinforcing rubber layer 6 should be set ina range of 94 to 99 of to JIS-A hardness, and an elastic modulus at 20°C. should be set in a range of 50 to 90 MPa.

[0021] Regarding a size of the reinforcing rubber layer 6, the followingrelational expressions should respectively be used as yardsticks fordetermining L₂/L₁ which is a ratio of a tire axial direction width L₂ ofthe reinforcing rubber layer 6 from a bead core innermost side face to atip of the bead toe section with respect to a tire axial directionmaximum width L₁ of the bead core 2, an angle θ which is made by a tireinner wall surface 10 of the tip part of the bead section and a beadseat 11, and H/L₁ which is a ratio of a height H (tread directionlength) of the reinforcing rubber layer 6 from a rim diameter equivalentposition with respect to the maximum width L₁.

0.5≦L ₂ /L ₁≦1.0

60≦θ

1.0≦H/L ₁

[0022] If L₂/L₁ is lower than 0.5, a width of the reinforcing rubberlayer (bead toe section) is too narrow to substantially improveturnability. On the other-hand, if L₂/L₁ exceeds 1.0, a width of thereinforcing rubber layer (bead toe section) is excessively large todeteriorate engagement between the bead section and the rim. If an angleθ is lower than 60°, since a capacity of the reinforcing rubber layer 6is reduced, a compressive strength of the reinforcing rubber layer 6 isalso reduced to make it impossible to improve turnability. If the angleθ exceeds 80°, the capacity of the reinforcing rubber layer 6 isincreased so as not to improve turnability. Accordingly, the angle θshould be in a range of 60° to 80°. If H/L₁ is equal to or lower than1.0, the capacity of the reinforcing rubber layer 6 is reduced to resultin a smaller compressive strength of the same. If H/L₁ exceeds 2.0, thecompressive strength is nearly saturated. Accordingly, H/L₁ should be ina range of 1.0 to 2.0.

EXAMPLE 1

[0023] {circle over (1)} We manufactured a tire 1 of the presentinvention and conventional tires 1 and 2 which all had equal tire sizesof 340/40 ZR13. Then, we examined turnability during high speed runningfor these tires. Table 1 shows results of the examination.

Tire 1 of the Present Invention

[0024] This tire has a bead section structure shown in FIG. 1. A beadcore 2 is a bead core made of single strand steel. A reinforcing rubberlayer 6 is made of short fiber reinforced rubber which has the followingcontent.

[0025] The short fiber used is an aromatic polyamide fiber which has anaverage length of 3.0 mm in a longitudinal direction and an averagediameter of about 10μA . Hardness of the reinforcing rubber layer 6 isequal to 98° of JIS-A hardness, and an elastic modulus at 20° C. is 85MPa.

Conventional Tire 1

[0026] This tire has the same structure as that of the tire 1 of thepresent invention except not using of short fibers.

Conventional Tire 2

[0027] This tire has the same structure as that of the tire 1 of thepresent invention except for the fact that a rubber stock havinghardness equal to 90° of JIS-A hardness is arranged as a reinforcingrubber layer 6 of a bead toe section 4, and a chafer composed of anorganic fiber cord is arranged in the outside of this rubber stock.

Turnability During High Speed Running

[0028] We carried out turnability tests by counting lap time when avehicle was run on a test course having one-round length of 4.4 km and acorner of a 100 m radius, and determining passing speeds at the cornerof a 100 m radius. An examined vehicle was a 3-litter car specializedfor racing. Results of the examination are indicated by indices with anindex of the conventional tire 2 set to 100. A larger index value meansbetter turnability. TABLE 1 Tire 1 of the Conventional tire Conventionaltire present invention 1 2 Turnability 110 100 100

[0029] It can be understood from Table 1 that the tire 1 of the presentinvention has better turnability compared with the conventional tires 1and 2.

[0030] {circle over (2)} For the tire 1 of the present invention, weexamined turnability during high speed running by setting θ to 60° andH/L₁ to 1.5, and sequentially changing L₂/L₁ to 0.25, 0.5. 0.75 and 1.0.A result of the examination is shown in FIG. 2. It should be noted thatan index of the convention tire 2 is 100 in FIG. 2.

[0031] It can be understood from FIG. 2 that indices of turnability arehigher when L₂/L₁ is set in the range of 0.5 to 1.0.

[0032] {circle over (3)} For the tire 1 of the present invention, weexamined turnability during high speed running by setting L₂/L₁ to 0.5and H/L₁ to 1.5, and sequentially changing θ to 50°, 60°, 70°, 80° and90°. A result of the examination is shown in FIG. 3. It should be notedthat an index of the conventional tire 2 is 100 in FIG. 3.

[0033] It can be understood from FIG. 3 that indices of turnability arehigher when θ is set in the range of 60° to 80°.

[0034] {circle over (4)} For the tire 1 of the present invention, weexamined turnability during high speed running by setting L₂/L₁ to 0.5and θ to 60°, and sequentially changing H/L₁ to 0.5, 1.0, 1.5 and 2.0. Aresult of the examination is shown in FIG. 4. It should be noted that anindex of the conventional tire 2 is 100 in FIG. 4.

[0035] It can be understood from FIG. 4 that indices of turnability arehigher in the range of 1.0<H/L₁.

[0036] (2) FIG. 5 is a sectional view of a tire meridian direction,showing one side of a bead section of another pneumatic tire of thepresent invention used as a racing tire. Regarding a bead section likethat shown in FIG. 5, a pair of such bead sections 1 are provided inboth left and right sides. Two carcass layers 3 ₁ and 3 ₂ are put arounda bead core 2 which is buried in the bead section 1. An end part of theinnermost carcass layer 3 ₁ is folded around the bead core 2 from a tireinner side to an outer side and wound up. The end part of the carcasslayer 3 ₁ is then positioned in the middle part of a bead filler 8. Onthe other hand, the outermost carcass layer 3 ₂ is arranged along andoutside the wound-up part of the carcass layer 3 ₁ to reach a tip of abead toe section 4. In a tread section, a plurality of belt layers (notshown) are arranged outside the carcass layers 3 ₁ and 3 ₂ and around atire. Reference numerals 7 ₁ and 7 ₂ denote reinforcing layers which aremade of general organic cords such as nylon fiber cords, polyester fibercords or the like.

[0037] In an area from the bead toe section 4 along a tire inner wallsurface, a reinforcing rubber layer having hardness set in a range of90° to 99° of JIS-A hardness is arranged. If hardness is lower than 90°of JIS-A hardness, the bead toe section 4 is too soft to improve highspeed turnability. On the other hand, if hardness exceeds 99° of JIS-Ahardness, rigidity of the bead section is excessively high to make itdifficult to perform mounting. Consequently, a bead toe cutting ordeterioration of seating of the bead section on the rim occurs.

[0038] An outer side of a reinforcing rubber layer 6 (including a tireaxial direction inner side face and a tire radial direction inner sideface of the reinforcing rubber layer 6) is covered with a chafer 13 froma tire inner side wall surface 10 to a bead seat 11. This chafer 13 iscomposed of an organic fiber cord which has a strength of 0.25 KN/cordor higher and an elastic modulus of 20 KN/mm² or higher.

[0039] The organic fiber cord of the chafer 13 has a high strength of0.25 KN/cord or higher and a high elastic modulus of 20 KN/mm² orhigher. This cord is made of, for example, one selected from an aromaticpolyamide fiber, a carbon fiber, a glass fiber, and so on. Among thesefibers, the aromatic polyamide fiber should preferably be used for thecord. Such an organic fiber cord should have a thickness of 720d/2 orhigher, preferably a thickness set in a range of 1000d/2 to 1500d/2. Thenumber of cords to be driven in (end count) for making the chafer shouldbe 29 pieces/50 mm or more, preferably 40 to 60 pieces/50 mm. Further,in the chafer, the organic fiber cord should preferably be inclined by20° to 90° in a tire circumferential direction.

[0040] Regarding a size of the reinforcing rubber layer 6, the followingrelational expressions should respectively be used as yardsticks fordetermining L₂/L₁ which is a ratio of a tire axial direction width L₂ ofthe reinforcing rubber layer 6 from a bead core innermost side face to atip of the bead toe section with respect to a tire axial directionmaximum width L₁ of the bead core 2, an angle θ which is made by a tireinner wall surface 10 side chafer of the tip part of the bead toesection and a chafer of the bead seat 11 side, and H/L₁which is a ratioof a height H (tread direction length) of the reinforcing rubber layer 6from a rim diameter equivalent position with respect to the maximumwidth L₁.

0.5≦L ₂ /L ₁≦1.0

60°≦θ

1.0≦H/L ₁

[0041] If L₂/L₁ is lower than 0.5, a width of the reinforcing rubberlayer (bead toe section) is too narrow to substantially improveturnability. On the other hand, if L₂/L₁ exceeds 1.0, a width of thereinforcing rubber layer (bead toe section) is excessively large todeteriorate engagement between the beat section and the rim. If an angleθ is lower than 60°, since a capacity of the reinforcing rubber layer 6is reduced, a compressive strength of the reinforcing rubber layer 6 isalso reduced to deteriorate turnability. If an angle θ exceeds 80°, acapacity of the reinforcing rubber layer 6 is too large to improveturnability. Accordingly, an angle θ should be in the range of 60° to80°. If H/L₁ is equal to or lower than 1.0, a capacity of thereinforcing rubber layer 6 is reduced to result in a smaller compressivestrength of the same. If H/L₁ exceeds 2.0, a compressive strength isnearly saturated. Accordingly, H/L₁ should be in the range of over 1.0to 2.0.

EXAMPLE 2

[0042] {circle over (1)} We manufactured a tire 2 of the presentinvention and a conventional tire 3, which had equal tire size of 340/40ZR13. For these tires, we examined turnability during high speed runningas in the case of the Embodiment 1. Table 2 shows results of theexamination.

Tire 2 of the Present Invention

[0043] This tire has a bead section structure shown in FIG. 5. A beadcore 2 is a bead core made of single strand steel. A reinforcing rubberlayer 6 has a rubber composition of the following content.

[0044] Hardness of the reinforcing rubber layer 6 is equal to 91° ofJIS-A hardness. A chafer 13 is composed of an aramid fiber cord(aromatic polyamide fiber cord) having a thickness of 1000d/2. An endcount is 41 pieces/50 mm. An inclination angle of the aramid fiber cordin a tire circumferential direction is 45°. L₂/L₁ is 0.5. An angle θ is60°. H/L₁ is 1.

Conventional Tire 3

[0045] This tire has the same structure as that of the tire 2 of thepresent invention except not having a chafer 13. TABLE 2 Tire 2 of thepresent invention Conventional tire 3 Turnability 110 100

[0046] It can be understood from Table 2 that the tire 2 of the presentinvention has better turnability compared with the conventional tire 3.

[0047] {circle over (2)} For the tire 2 of the present invention, weexamined turnability during high speed running by setting θ to 60° andH/L₁ to 1.5, and sequentially changing L₂/L₁ to 0.25, 0.5, 0.75 and 1.0.A result of the examination is shown in FIG. 6. It should be noted thatan index of the conventional tire 3 is 100 in FIG. 6.

[0048] It can be understood from FIG. 6 that turnability indices arehigher when L₂/L₁ is set in the range of 0.5 to 1.0.

[0049] {circle over (3)} For the tire 2 of the present invention, weexamined turnability during high speed running by setting L₂/L₁ to 0.5and H/L₁ to 1.5, and sequentially changing θ to 50°, 60°, 70°, 80° and90°. A result of the examination is shown in FIG. 7. It should be notedthat an index of the conventional tire 3 is 100 in FIG. 7.

[0050] It can be understood from FIG. 7 that turnability indices arehigher when θ is set in the range of 60° to 80°.

[0051] {circle over (4)} For the tire 2 of the present invention, weexamined turnability during high speed running by setting L₂/L₁ to 0.5and θ to 60°, and sequentially changing H/L₁ to 0.5, 1.0, 1.5 and 2.0. Aresult of the examination is shown in FIG. 8. It should be noted that anindex of the conventional tire 3 is 100 in FIG. 8.

[0052] It can be understood from FIG. 8 that turnability indices arehigher in the range of 1.0≦H/L₁.

[0053] As described above, according to the present invention, the beadsection includes (1) the reinforcing rubber layer made of short fiberreinforced rubber, or (2) the reinforcing rubber layer having hardnessset in the range of 90° to 99°, which is arranged in the area from thebead toe section along the tire inner wall surface. Also, from the tireinner wall surface to the bead seat area, the outer side of thereinforcing rubber layer is covered with the chafer, which is composedof an organic fiber cord having a strength of 0.25 KN/cord or higher andan elastic modulus of 20 KN/mm2 or higher (high strength and highelastic modulus organic fiber cord). Therefore, high-speed turnabilitycan be secured, for example, when a vehicle is turned on a corner of a100 m radius during running at a high speed of 200 km/h or higher.

What is claimed is:
 1. A pneumatic tire comprising: carcass layersprovided between a pair of bead cores buried one in a left bead sectionand the other in a right bead section; and a belt layer arranged outsidesaid carcass layers and around a tire in a tread section; wherein areinforcing rubber layer made of short fiber reinforced rubber isarranged in an area of said bead section from a bead toe section along atire inner wall surface.
 2. A pneumatic tire according to claim 1 ,wherein a short fiber for said short fiber reinforced rubber is selectedfrom the group consisting of a polyester fiber, a nylon fiber, a vinylonfiber, a carbon fiber, a glass fiber and an aromatic polyamide fiber. 3.A pneumatic tire according to claim 2 , wherein a length of said shortfiber in a longitudinal direction is set in a range of 0.2 mm to 6.0 mm,and an average diameter of said short fiber is set equal to or lowerthan 15μ.
 4. A pneumatic tire according to claim 1 , wherein a shortfiber in said reinforcing rubber layer is mainly oriented in a tireradial direction.
 5. A pneumatic tire according to claim 1 , whereinhardness of said reinforcing rubber layer is set in a range of 94 to 99of JIS-A hardness, and an elastic modulus of said reinforcing rubberlayer at 20° C. is set in a range of 50 to 90 MPa.
 6. A pneumatic tireaccording to claim 1 , wherein said reinforcing rubber layer contains 5to 30 parts weight of short fiber blended with respect to 100 partsweight of rubber.
 7. A pneumatic tire according to claim 1 , wherein thefollowing relational expressions are respectively used as yardsticks fordetermining L₂/L₁ which is a ratio of a tire axial direction width L₂ ofsaid reinforcing rubber layer from a bead core innermost side face to atip of said bead toe section with respect to a tire axial directionmaximum width L₁ of said bead core, an angle θ which is made by a tireinner wall surface of a tip part of said bead toe section and a beadseat, and H/L₁ which is a ratio of a height H of said reinforcing rubberlayer from a rim diameter equivalent position with respect to saidmaximum width L₁: 0.5≦L ₂ /L ₁≦1.060°≦θ1.0≦H/L ₁
 8. A pneumatic tireaccording to claim 7 , wherein said angle θ is set in a range of 60° to80°.
 9. A pneumatic tire according to claim 7 , wherein said ratio H/L₁is set in a range of over 1.0 to 2.0.
 10. A pneumatic tire comprising:carcass layers provided between a pair of bead cores buried one in aleft bead section and the other in a right bead section; and a beltlayer arranged outside said carcass layers and around a tire in a treadsection; wherein a reinforcing rubber layer is arranged in an area ofsaid bead section from a bead toe section along a tire inner wallsurface, said reinforcing rubber layer having hardness set in a range of90° to 99° of JIS-A hardness, and a chafer composed of an organic fibercord is provided to cover an outer side of said reinforcing rubber layerfrom said tire inner wall surface to a bead seat area, said organicfiber cord having a strength of ≦0.25 KN/cord, and an elastic modulus of≦20 KN/mm².
 11. A pneumatic tire according to claim 10 , wherein anorganic fiber for said organic fiber cord is selected from the groupconsisting of an aromatic polyamide fiber, a carbon fiber and a glassfiber.
 12. A pneumatic tire according to claim 10 , wherein a thicknessof said organic fiber cord is set in a range of 1000d/2 to 1500d/2, andan end count of said organic fiber cords is set in a range of 40 to 60pieces/50 mm.
 13. A pneumatic tire according to claim 10 , wherein insaid chafer, said organic fiber cord is inclined in a tirecircumferential direction by 20° to 90°.
 14. A pneumatic tire accordingto claim 10 , wherein the following relational expressions arerespectively used as yardsticks for determining L₂/L₁ which is a ratioof a tire axial direction width L₂ of said reinforcing rubber layer froma bead core innermost side face to a tip of said bead toe section withrespect to a tire axial direction maximum width L₁ of said bead core, anangle θ which is made by a tire inner wall surface side chafer of a tippart of said bead toe section and a bead seat side chafer, and H/_(L)which is a ratio of a height H of said reinforcing rubber layer from arim diameter equivalent position with respect to said maximum width L₁:0.5≦L ₂ /L ₁≦1.060°≦θ1.0<H/L ₁
 15. A pneumatic tire according to claim14 , wherein said angle θ is set in a range of 60° to 80°.
 16. Apneumatic tire according to claim 14 , wherein said ratio H/L₁ is set ina range of over 1.0 to 2.0.